ADT 2005 has many powerful new features that others will demonstrate better than I but these are a few simple, but useful, enhancements I've found worthwhile. Not "big ticket items" but things I use constantly:
(click on thumbnails for a larger image)
1) Space Creation Options:
Insert: "Traditional" ADT space placement.
Rectangle; Select 2 points to create a rectangular shape.
Polygon: Allows you to draw irregular shapes, including arc segments, while creating the space.
2) Space grips: These allow quick editing of existing shapes:
~ Add or remove Vertices.
~ Drag edge with dimension input.
~ Add Vertex & create new straight edge.
~ Add Vertex & create new arc edge.
~ I have also noticed that merged spaces are a lot cleaner as the redundant vertices that used to be left where aligned edges overlapped are no longer created.
4) Maximise Layout Viewport: Click to have a layout viewport grow to fill the work area for editing. Zoom & pan to edit as if model space. Click again & it reverts to the previous size on the layout. This is great when editing in layouts which I prefer.